1. Field of the Invention
This invention relates to a device and method for aligning an optical fibre with an optical device in an opto-electronic package.
2. Description of the Prior Art
Coupling efficiency between an optical fibre and an optical device, which may be an optical transmitter, or an optical receiver, is limited by the accuracy and stability of the alignment achievable during the assembly process.
Conventionally, the optical device is securely mounted in an opto-electronic package. Subsequently an optical fibre, which is usually mounted in a support tube, is aligned to the optical device. The tube is then secured to the package, for example, by soldering or welding the tube to the package. Laser welding is usually employed as it has many advantages over soldering such as no joint material, accurate position of weld spots, localised heating, no creep and more robust mode of attachment. However, a disadvantage of the support tube/laser weld technique is that of Post Weld Shift (PWS) Post weld shift occurs as a result of the contraction of the laser spot welds, and can cause the fibre to move (misalign) with respect to the optical device.
One way of achieving the alignment of an optical fibre and an optical device is by placing the optical fibre using a feature which has been etched onto a silicon optical bench, upon which an optical device has already been precisely attached. However, this simple technique is limited in precision by the manufactured accuracy of the silicon, the placement of the optical device and subsequent movement of the fibre when securing the fibre to the silicon bench. (The method of securing the fibre to the silicon bench usually involves a thermal process (e.g. soldering, adhesive curing) and due to material mismatch and differential coefficients of expansion, fibre movement can often occur.
An alternative technique uses a deformable mount to support the optical fibre. Once the optical device and the optical fibre have been aligned and attached to the package, the mount is mechanically deformed until an optimum coupling efficiency is achieved.
However, this technique suffers from the disadvantage that the deformable mount is usually only substantially deformable in one plane, and if the distance between the optical fibre and the optical device is affected by factors such as PWS, fibre attachment or deformable mount attachment, then there is no remedial action which may be taken.
In many optical applications, it is desirable for the optical fibre and optical device to be mounted as closely together as possible to maximise coupling efficiency. For example the distance required may be as little as one micron, whereas PWS can cause up to twenty to thirty microns of movement.
The present invention seeks to alleviate the above mentioned problems